This invention relates to an electrophotographic sensitive material useful advantageously in an image-forming apparatus such as the copying machine.
In recent years, as electrophotographic sensitive materials for use in such image-forming apparatuses as copying machines, sensitive materials of the kind permitting a wide freedom in design of functions have been proposed.
Particularly, electrophotographic sensitive materials possessed of a photosensitive layer of the separate function type containing an electric charge generating material capable of generating electric charge upon exposure to light and an electric charge transferring material capable of transferring generated electric charge in one or two layers have been proposed. For example, electrophotographic sensitive materials possessed of a single-layer type photosensitive layer containing an electric charge generating material, an electric charge transferring material, and a binding resin in one layer and electrophotographic sensitive materials possessed of a laminate type photosensitive layer formed by superposition of an electric charge generating layer containing an electric charge generating material on an electric charge transferring layer containing an electric charge transferring material and a binding resin have been proposed.
In the formation of a copied image by the use of an electrophotographic sensitive material, the Carlson process is popularly utilized. The Carlson process basically comprises a charging step for uniformly charging a sensitive material by corona discharge, an exposing step for exposing the charged sensitive material through a given original image to light thereby forming on the sensitive material an electrostatic latent image conforming to the original image, a developing step for developing the electrostatic latent image with a developer containing a toner thereby forming a toner image, a transferring step for causing the toner image to be transferred onto a substrate such as paper, a fixing step for fixing the toner image transferred on the substrate, and a cleaning step for removing the toner remaining on the sensitive material after the transferring step. For the image to be produced with high quality in the Carlson process, the electrophotographic sensitive material is required to excel in the charging property and the photosensitive property and, at the same time, to be low in residual potential after the exposure to light.
The electrophotographic properties of the electrophotographic sensitive material of the separate function type mentioned above are affected in a large measure by the combination of an electric charge generating material and an electric charge transferring material. For example, an electrophotographic sensitive material possessed of a photosensitive layer using a pyrrolopyrrole type compound proposed as an electric charge generating material U.S. Pat. No. 4,632,893 in combination with a hydrazone type compound such as N-ethyl-3-carbazolylaldehyde-N,N-diphenyl hydrazone which depends heavily for drift mobility upon the intensity of electric field is high in residual potential and is deficient in sensitivity. The hydrazone type compound has no sufficient stability to resist light because it is liable to be isomerized and dimerized on exposure to light. The sensitive material, therefore, has a disadvantage that it suffers from gradual decrease of sensitivity and gradual increase of residual potential through repeated rounds of printing.
A sensitive material which uses a phthalocyanine type compound as an electric charge generating material in combination with a styryl triphenylamine type compound represented by 4-styryl-4'-methoxy triphenylamine, 4-(4-methylstyryl)-4'-methyl triphenylamine, or 4-(3,5-dimethylstyryl)-4'-methyl triphenylamine as an electric charge transferring material has been proposed (Publication for unexamined Japanese Patent Application Disclosure No. 115,167/1987).
The sensitive material possessed of a photosensitive layer containing a styryl triphenylamine type compound generally excels in electrical properties and sensitive properties as compared with the sensitive material containing other electric charge transferring material.
The styryl triphenylamine type compound, however, exhibits no sufficient compatibility with a binding resin, possesses a small capacity for electron donation, and betrays its deficiency in the electric charge transferring property. The sensitive material which is produced by using the styryl triphenylamine type compound, therefore, has a disadvantage that the charging property and the sensitivity are short of sufficiency and the residual potential is unduly high.